Synthesis and study of electroactive nanoparticles and their polymer composites for novel applications

Polymer ceramic composites using a polymer binder, nanosized BaTiO₃ and metal particles were developed for radiation shielding in the microwave region. From X-ray Diffraction (XRD) the crystallinity and nanosize of BaTiO₃ was confirmed in the composite. Interesting changes in Differential Scanning Calorimetry (DSC) were observed before and after ball milling of BaTiO₃. Shielding Efficiency (SE) of microwave radiation has been measured from transmitted fraction (TF) of electromagnetic waves (EM) at different frequencies. The changes in TF were assigned to reflection and absorption of EM waves in different composites.     

Availability of water glass/Bi2O3 composites in dielectric and gamma-ray screening applications

ABSTRACT

Sodium silicate (Na₂Si₃O₇) also known as water glass is a very low cost material which is used in many industrial applications such as a builder in detergents, as a binder and adhesive etc. But so far the electrical properties of sodium silicate and its ability to screen radiation have never been investigated. In the present study, the frequency dependent electrical properties and gamma-ray shielding performance of water glass based bismuth oxide composites have been studied for the first time. In accordance with this purpose, Na₂Si₃O₇/Bi₂O₃ glassy composites have been prepared for searching their possible applications in electronics and radiation screening. The surface morphology of the samples have been determined by Scanning Electron Microscope (SEM). The frequency dependent electrical properties such as complex impedance, complex dielectric function and conductivity have been analyzed at room temperature between 1 and 40?MHz. As a result of alternative current (ac) electrical analysis, it has been determined that the Na₂Si₃O₇/Bi₂O₃ composites can be utilized as a dielectric layer in capacitors. On the other hand, since bismuth oxide is an anti-radiative material, the gamma-ray screening parameters such as mass attenuation coefficient, half layer and tenth layer values along with mean free path of the composites have been defined experimentally by using NaI(Tl) scintillation detector for the Ba-133 radiation source at 81 and 356?keV. The values of these parameters have also been checked by Monte–Carlo simulation. Since a good agreement has been assigned between experimental and Monte–Carlo simulation results, the related gamma ray shielding parameters have been determined by Monte–Carlo simulation for other gamma photon energies (140?keV, 208?keV, 468?keV, and 661?keV) which are generated from Tc-99, Lu-177, Ir-132, and Cs-137 sources. Ultimately, Na₂Si₃O₇/Bi₂O₃(35%) composite has been suggested as an eco-friendly, lead-free glassy structured material for the gamma radiation shielding in medical applications.     

Comparison of radiation shielding ratios of nano-sized bismuth trioxide and molybdenum

In this study, radiation shielding fibers using non-hazardous nano-sized bismuth trioxide and molybdenum instead of lead were developed and evaluated. Among the elements with high densities and atomic numbers, non-hazardous elements such as bismuth trioxide and molybdenum were chosen as a shielding element. Then, bismuth trioxide (Bi₂O₃) with average particle size 1–500?µm was ball milled for 10?min to produce a powdered form of nanoparticles with average particle size of 10–100?nm. Bismuth trioxide nanoparticles were dispersed to make a colloidal suspension, followed by spreading and hardening onto one or two sides of fabric, to create the radiation shielding fabric. The thicknesses of the shielding sheets using nano-sized bismuth and molybdenum were 0.4 and 0.7?mm. According to the lead equivalent test of X-ray shielding products suggested by KS, the equivalent dose was measured, followed by calculation of the shielding rate. The shielding rate of bismuth with 0.4?mm thickness and at 50?kVp was 90.5%, which is comparable to lead of 0.082?mm thickness. The shielding rate of molybdenum was 51.89%%, which is comparable to lead of 0.034?mm. At a thickness of 0.7?mm, the shielding rate of bismuth was 98.73%, equivalent to 0.101?mm Pb, whereas the shielding rate of molybdenum was 74.68%, equivalent to 0.045?mm?Pb. In conclusion, the radiation shielding fibers using nano-sized bismuth developed in this study are capable of reducing radiation exposure by X-ray and its low-dose scatter ray.     

Ultrasonic desulfurization of amphiphilic magnetic-Janus nanosheets in oil-water mixture system

Fe₃O₄ was obtained by reacting FeCl₂ and FeCl₃ with polyethylene glycol, and labeled onto a amphiphilic Janus nanosheet. It was confirmed by infrared spectroscopy, SEM, AFM and EDS that the Fe₃O₄ nanoparticles changed from hydrophilic to amphiphilic. The oxidative desulfurization performance of amphiphilic iron oxide was studied. Results showed that the Janus nanosheets labeled with Fe₃O₄ could significantly improve the removal rate of thiophene sulfide in simulated oil synergistically with ultrasonic waves, and the desulfurization rate could reach 100%. Further, the effect of ultrasound on the sensing ability of the oil–water interface was studied and the ultrasonic attenuation coefficient was calculated. In addition to the desulfurization mechanism of Fe₃O₄, it was found that although the ultrasonic attenuation coefficient of the amphiphilic nanosheets was high, the number of hydroxyl radicals determined the desulfurization efficiency. The amphiphilic Fe ions were more favorable for the formation of hydroxyl radicals than the single hydrophilic ones.     

Tuning of electromagnetic wave absorbing properties in Fe-deficient SrFe9.6-xCo1.2Ti1.2O19 hexaferrite-epoxy composites

We report the tunable electromagnetic (EM) wave absorption properties of Fe-deficient SrFe_9.6-xCo_1.2Ti_1.2O₁₉ hexaferrite–epoxy composites. SrFe_9.6-xCo_1.2Ti_1.2O₁₉ hexaferrite powders were prepared via solid-state reaction routes. It was observed that Sr–Ti-rich second phases were formed as x increased, i.e., the Fe content decreased. The ferromagnetic resonance (FMR) frequency of the composites gradually decreased from 8.8 GHz to 4.8 GHz with increasing x, and accordingly, the EM absorption frequency range also gradually changed. The gradual FMR frequency shift was attributed to the compositional shift in the mother phase. It is predicted that the Fe deficiency caused a decrease in the magnetocrystalline anisotropy, and in turn, it shifted the FMR frequency and modified the corresponding EM absorbing properties. All the samples demonstrated a high EM absorption performance with the lowest reflection loss of < −40 dB at the optimized frequency and thickness.     

Magnetic and electromagnetic absorption properties of FeNi alloy nanoparticles supported by reduced graphene oxide

FeNi alloy nanoparticles (NPs) supported by reduced graphene oxide (RGO) (FeNi/RGO nanocomposites) were successfully synthesized through in‐situ reduction. Large amounts of sphere‐like FeNi NPs are uniformly deposited on the RGO nanosheets. The magnetic hysteresis measurement reveals the ferromagnetic behavior of the nanocomposites at room temperature. According to the electromagnetic (EM) characteristics, the FeNi/RGO nanocomposites show outstanding EM absorption properties in the 2–18 GHz range, as evidenced by the wide effective absorption bandwidth (up to 3.3 GHz, with reflection loss R_L < –10 dB) and a minimal R_L (–32 dB) at 12.4 GHz with a thickness of 1.5 mm. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Very high-frequency gravitational waves from magnetars and gamma-ray bursts

Extremely powerful astrophysical electromagnetic(EM) systems could be possible sources of highfrequency gravitational waves(HFGWs). Here, based on properties of magnetars and gamma-ray bursts(GRBs), we address "Gamma-HFGWs"(with very high-frequency around 10~(20) Hz) caused by ultra-strong EM radiation(in the radiation-dominated phase of GRB fireballs) interacting with super-high magnetar surface magnetic fields(～10~(11) T).By certain parameters of distance and power, the Gamma-HFGWs would have far field energy density ?gw around10~(-6), and they would cause perturbed signal EM waves of～10~(-20) W/m~2 in a proposed HFGW detection system based on the EM response to GWs. Specially, Gamma-HFGWs would possess distinctive envelopes with characteristic shapes depending on the particular structures of surface magnetic fields of magnetars, which could be exclusive features helpful to distinguish them from background noise. Results obtained suggest that magnetars could be involved in possible astrophysical EM sources of GWs in the very high-frequency band, and Gamma-HFGWs could be potential targets for observations in the future.     

Electromagnetic shielding of multiwalled,bamboo-like carbon nanotube/methyl vinyl silicone composite prepared by liquid blending

Multiwalled, bamboo-like carbon nanotube (BCNT)/methyl vinyl silicone (MVQ) composites with different concentrations of BCNT were fabricated by liquid blending method with an aim to investigate the behavior of such composites as effective electromagnetic interference shielding material in the frequency range of 1–6?GHz. The morphology and structure of BCNT were characterized and elucidated. Scanning electron microscopy examination showed that the BCNTs homogeneously dispersed in MVQ. The electrical conductivity (σ) and shielding effectiveness (SE) of the composite were measured and discussed. The results showed that the BCNTs/MVQ composites had a relatively low percolation threshold at 0.92?wt. % BCNT, and the σ showed a decreasing linear relation with temperature, i.e., the σ slightly decreased with increasing temperature. The BCNTs/MVQ composites with SE of 33–38?dB were obtained at 7?wt. % BCNT loading. Shielding mechanism was studied by resolving the total incident energy into absorbed, reflected, and transmitted contribution, and the result showed that the dominated shielding mechanism was reflection loss.     

Facile decolorization of methylene blue by morphology-dependence δ-MnO2 nanosheets -modified diatomite

In this work, coscinodiscus-diatomite and melosira-diatomite have been decorated by ultrathin birnessite MnO₂ (δ-MnO₂) nanosheets through a one-pot hydrothermal method without using any surfactants. The δ-MnO₂ nanosheets are observed to grow vertically on the purified melosira-diatomite as well as coscinodiscus-diatomite. Moreover, the two composites exhibit high efficiency for decomposing methylene blue (MB) in the presence of H₂O₂. The coscinodiscus-diatmite@MnO₂ achieves a removal rate of 81.8% (2 h), and yet melosira-diatomite@MnO₂ reaches a higher degradation rate of 91.3% in 2 h. Additionally, the effects of catalyst amount, catalysis reaction temperature, preparing time have also been investigated. In principle, the diverse diatomite@MnO₂ nanostructures not only present an environmentally friendly and low cost with a good cycling stability, but also offer a simple way for the catalytic degradation of dye waste water in practical applications.     

One-step synthesis of Fe3O4 nanorods/graphene nanocomposites

A composite of graphene (GE) supported by rod-like Fe₃O₄ nanocrystals has been fabricated by a simple one-step chemical route. X-ray diffraction and transmission electron microscopy results show that the Fe₃O₄ nanorods with diameters in the range of 15?C20 nm and lengths of 150?C200 nm were firmly assembled on the GE nanosheet surface. Magnetic property investigation indicated that the Fe₃O₄/GE composites exhibit a ferromagnetic behavior and possess a saturation magnetization of 50.11?emu?g^?1. Moreover, Fe₃O₄/GE composites showed a very high adsorption capacity of Congo red.     

Preparation of Co3O4 nanoplate/graphene sheet composites and their synergistic electrochemical performance

Co₃O₄ nanoplate/graphene sheet composites were prepared through a two-step synthetic method. The composite material as prepared was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The platelet-like morphology of Co₃O₄ leads to a layer-by-layer-assembled structure of the composites and a good dispersion of Co₃O₄ nanoplates on the surface of graphene sheets. The electrochemical characteristics indicate that the specific capacitance of the composites is 337.8 F?g^?1 in comparison with the specific capacitance of 204.4 F?g^?1 without graphene sheets. Meanwhile, the composites have an excellent rate capability and cycle performance. The results show that the unique microstructure of the composites enhances the electrochemical capacitive performance of Co₃O₄ nanoplates due to the three-dimensional network of graphene sheets for electron transport increasing electric conductivity of the electrode and providing unobstructed pathways for ionic transport during the electrochemical reaction.     

Controlled deposition of covalently bonded tantalum oxide on carbon supports by solvent evaporation sol-gel process

A simple strategy for covalently attaching Ta₂O₅ particles onto functionalized graphitic carbon supports has been developed to fabricate hybrid nanocomposites. In this process, tantalum ethoxide was directly reacted with functional groups on the carbon surface to form covalent bonding, which caused the carbonyl stretches of the carbon supports to be blue-shifted to 50-70 cm⁻¹ after Ta₂O₅ particle deposition. Homogeneously deposited Ta₂O₅ particles on the carbon supports have been studied by X-ray diffraction (XRD), FT-IR spectroscopy, scanning electron microscopy (SEM), and transmission electron microscope (TEM).     

Self-assembly of metal–organic frameworks and graphene oxide as precursors for lithium-ion battery applications

We fabricated composites of Fe₂O₃/reduced graphene oxide as lithium-ion batteries anode material with controlled structures by employing self-assembly of metal–organic frameworks (MOFs) and polymer-functionalized graphene oxide as precursors. By electrostatic interaction, the negatively charged MOFs, Prussian Blue (PB), are assembled on poly(diallyldimethylammonium chloride) (PDDA)-functionalized graphene oxide (positive charge). Then the PB cubes become FeOOH nanosheets when treated with sodium hydroxide. Upon further annealing, the FeOOH nanosheets transform to Fe₂O₃ nanoparticles while the graphene oxide become reduced graphene oxide simultaneously. It was found that the composites have good performance as anode of lithium-ion battery. This work shows a new way for self-assembling MOFs and 2D materials.     

Synthesis and characterizations of microwave sintered ferrite powders and their composite films for practical applications

Phase pure single phase ferrite powders of (Ni_xR_1−x)_0.5Zn_0.5Fe₂O₄ (R=Mn, Co, Cu; x=0, 0.5) were manufactured using microwave sintering at 930 °C for 10 min in air atmosphere. The powders were characterized for their structure, microstructure, thermal, and magnetic properties. Selected powders were used as fillers to prepare their composite films using polymethyl methacrylate polymers as matrix. The composite films were prepared using the melt blending approach and were tested for their microstructure, thermal, and magnetic hysteresis loop as well as 3D magnetic field space mappings using an electromagnetic compatibility scanner. Among the studied ferrites, cobalt doped ferrites and their composites showed the best electromagnetic interference (EMI) shielding effectiveness value and have potential for practical EMI shielding applications.     

Synergistic effect of polypyrrole/BST/RGO/Fe3O4 composite for enhanced microwave absorption and EMI shielding in X-Band

Present study focus on the designing of high performance microwave absorbing material against electromagnetic pollution. Herein we synthesize conducting polymer based composite encapsulated with Barium strontium titanate (BST), reduced graphene oxide (RGO), and Fe₃O₄ nanoparticles via chemical oxidative polymerization of pyrrole. The synthesized composite materials were thoroughly characterized using SEM, FTIR, XRD, TGA, and VSM techniques. The presence of filler materials in conducting polymer matrix leads to absorption dominated shielding effectiveness value of 48 dB in the frequency range of 8.2–12.4 GHz (X-band). Moreover, presence of dielectric and magnetic fillers increases the thermal and chemical stability of the composite material. The obtained shielding effectiveness value is above the recommended limit (30–40 dB) required for the commercial applications, therefore these composite material could be used as effective shield against EM pollution.     

DC conductivity and magnetic properties of piezoelectric–piezomagnetic composite system

A series of composites (1−x) (Ni_0.8Zn_0.2Fe₂O₄)+x (BaTiO₃), where x=0%, 20%, 40%, 60%, 80% and 100% BT content, have been prepared by the standard ceramic technique, then sintered at 1200 °C for 8 h. X-ray diffraction analysis shows that the prepared composites consist of two phases, ferrimagnetic and ferroelectric. DC electrical resistivity, thermoelectric power, charge carriers concentration and charge carrier mobility have been studied at different temperatures. It was found that the DC electrical conductivity increases with increasing BT content. The values of the thermoelectric power were positive and negative for the composites indicating that there are two conduction mechanisms, hopping and band conduction, respectively. Using the values of DC electrical conductivity and thermoelectric power, the values of charge carrier mobility and the charge carrier concentration were calculated. Magnetic measurements (hysteresis loop and magnetic permeability) show that the magnetization decreases by increasing BT content. M–H loop of pure Ni_0.6 Zn_0.4 Fe₂O₄ composite indicates that it is paramagnetic at room temperature and that the magnetization is diluted by increasing the BT content in the composite system. The value of magnetoelectric coefficient for the composites decreases by increasing BT content for all the compositions except for 40% BT content, which may be due to the low resistivity of magnetic phase compared with the BT phase that causes a leakage of induced charges on the piezoelectric phase. Since both ferroelectric and magnetic phases preserve their basic properties in the bulk composite, the present BT–NZF composite are potential candidates for applications as pollution sensors and electromagnetic waves.     

Biosynthesis and magnetic properties of mesoporous Fe3O4 composites

Magnetic Fe₃O₄ materials with mesoporous structure are synthesized by co-precipitation method using yeast cells as a template. The X-ray diffraction (XRD) pattern indicates that the as-synthesized mesoporous hybrid Fe₃O₄ is well crystallized. The Barrett-Joyner-Halenda (BJH) models reveal the existence of mesostructure in the dried sample which has a specific surface area of 96.31 m²/g and a pore size distribution of 8-14 nm. Transmission electron microscopy (TEM) measurements confirm the wormhole-like structure of the resulting samples. The composition and chemical bonds of the Fe₃O₄/cells composites are studied by Fourier transform infrared (FT-IR) spectroscopy. Preliminary magnetic properties of the mesoporous hybrid Fe₃O₄ are characterized by a vibrating sample magnetometer (VSM). The magnetic Fe₃O₄/cells composites with mesoporous structure have potential applications in biomedical areas, such as drug delivery.     

Explosive instability of quasi-phonon triads in antiferromagnet under frequency modulated electromagnetic field

Compensation of nonlinear frequency shift of hybrid magnetoelastic waves (quasi-phonons) in the process of parametric three-boson coupling is studied theoretically and experimentally. The singular frequency modulation of electromagnetic pumping is proposed for the observation of explosive instability of quasi-phonon triads. The explosive supercritical dynamics is simulated theoretically on the basis of strong nonlinear equations of magnetoelastic dynamics and observed in α-Fe₂O₃ magnetoacoustic resonator.     

Fabrication of flower-shaped Bi2O3 superstructure by a facile template-free process

A novel flower-shaped Bi₂O₃ superstructure has been successfully synthesized by calcination of the precursor, which was prepared via a citric acid assisted hydrothermal process. The precursor and Bi₂O₃ were characterized with respect to morphology, crystal structure and elemental chemical state by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was shown that both the precursor and Bi₂O₃ flower-shaped superstructure were constructed of numerous nanosheets while the nanosheets consisted of a great deal of nanoparticles. Furthermore, key factors for the formation of the superstructures have been proposed; a mechanism for the growth of the superstructure has been presented based on the FESEM investigation of different growth stages.     

Preparation and characterization of inorganic colored coating layers on lamellar mica-titania substrate

The inorganic colored composite pigments, such as Fe₂O₃-, Bi₄Ti₃O₁₂-, and CoAl₂O₄-coated mica-titania composites, were prepared by hydrolysis of FeCl₃, Bi(NO₃)₃, and Co(NO₃)₂/Al(NO₃)₃ in the presence of mica-titania substrate and calcination at different temperatures. The inorganic coating layers on mica-titania substrate surfaces were explored by X-ray diffraction, scanning electron microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy. Dense and uniform Fe₂O₃ coating layers were formed on the surfaces of mica-titania substrates. At lower Bi₂O₃ loading, Bi₄Ti₃O₁₂ nanoparticles were formed on the surfaces of mica-titania substrates. But at higher Bi₂O₃ loading, Bi₄Ti₃O₁₂ nanosheets were formed and perpendicularly oriented to the substrate surfaces. CoAl₂O₄ nanosheets were formed on the mica-titania substrates and perpendicularly oriented to the substrate surfaces. The pigmentary performances of the inorganic composite pigments were analyzed by CIE, indicating that red, yellow, and blue colored pigments were achieved by coating Fe₂O₃, Bi₄Ti₃O₁₂, and CoAl₂O₄ on mica-titania substrate surfaces, respectively. The pigmentary performances of the inorganic composite pigments were significantly affected by the morphology and loading of inorganic coating layers.